Ext JS 4 is a JavaScript framework that provides resources to build Rich Internet Applications with great performance. Ext JS 4 has been packed with many new features and it is difficult to master, even for seasoned experts in Ext JS 3.
Ext JS 4 First Look teaches you the main functional areas of Ext JS 4 that have significant new features, explains the new features and how to use them, while highlighting the differences between Ext JS 4 and the previous versions.
This book will give you the knowledge to make the required changes to Ext JS 3 application to build a complete Ext JS 4 application.
This book provides examples of how to load Ext JS components by demand, charts, grid, tree, forms and panels, new data model, themes and mvc architecture.
Ext JS 4 First Look provides full examples and illustrations to help you easily learn the new features of Ext JS 4.

很高兴，今天发布了一个ExtJS 4.1的性能改善的预览版。在过去几个月，我们一直在努力地改善加载时间、渲染和整个框架内布局的性能，一直使用自己的例子和你们的应用程序做跨浏览器的基准测试和性能优化，并取得了一些显著的改进。

今天，我们将开放当前的生成包，让你的应用可以感受一下速度的提高。我们希望你们用该版本测试你们的应用陈旭，但要注意此版本的只是前期性质的版本，这只是一个预测试的性能预览版本且某些组件存问题。我们不建议在生产环境中使用，但我们很乐意听到在应用中有关加载、渲染和布局性能等方面的响应。